For many years, attempts have been made to remove or separate particular materials within waste materials in water through various reaction processes so that they may be converted or recycled to useful products. In doing so, many disclosures have utilized deep well reactors, known as gravity pressure vessels (GPVs), to aid in the removal or separation of dissolved and non-dissolved organic materials and the like. By using a GPV, the operator can increase the speed and efficiency of the reaction processes employed therein.
For example, it is well known that the speed and efficiency of wet combustion (also known as “wet oxidation”) of certain organic materials can be increased by conducting this reaction process in water at elevated temperatures and pressures such as may be provided by a GPV. In wet oxidation, oxygen reacts with organic materials that have been dissolved in water. U.S. Pat. Nos. 3,853,759 and 4,792,408, incorporated herein by reference, both disclose the use of oxygen, either present in the waste materials in water themselves, or supplied to the process stream via an external source, to promote the exothermic reaction of various waste materials at or near a reaction chamber in the bottom of a GPV. The heat energy created by the oxidation reaction in the bottom chamber of the GPV is then used to convey heat energy outward from the process stream as it flows upward through the center of the GPV to the incoming process stream surrounding the upward flow for further reaction, thereby providing an essentially self-sustaining pre-heating of the incoming process stream into the reaction chamber, with any excess being realized at the surface outlet. It will be appreciated that any heat energy lost in such a process will be attributable to the terminal temperature difference in the water after processing and any heat energy loss to the strata.
Likewise, it is well known that the speed and efficiency of weak acid hydrolysis of certain other, different organic materials can be increased by conducting this process in water at elevated temperatures and pressures, again as may be provided by a GPV. To induce weak acid hydrolysis within a GPV, an acid is injected into an endothermic reaction chamber of the GPV, typically positioned within the updraft flow of the process stream. Current GPV technology uses a flow accelerated reaction chamber, which induces and quenches hydrolysis of the materials quickly and effectively. For example, U.S. Pat. Nos. 5,711,817 and 5,879,637, incorporated herein by reference, disclose the conversion of cellulosic material to ethanol by acid hydrolysis of the cellulosic material at elevated temperatures and pressures with a GPV, and fermenting the product thereof. However, in order to sustain the endothermic reaction, i.e., hydrolysis, as set forth in these earlier patents, enough added heat energy, typically in the form of steam and hot water supplied from an external source, must have been supplied to the process stream prior to the reaction in order for the reaction to be effective. The addition of this heat energy to a GPV required to sustain the endothermic reaction detracts from the usefulness of the process, and makes it much less cost effective. Moreover, there are environmental aspects involved with the generation of external heat energy that may also be disadvantageous.
Furthermore, in addition to the need for added external heat energy to conduct the hydrolysis reaction, it is known that weak acid hydrolysis of certain waste materials within a GPV results in the creation of useless by-products that must be discarded, destroyed, mitigated, or left to contaminate the atmosphere or water upon completion of the reaction. Attempting to rid the processed stream of these by-products after processing further limits the usefulness, efficacy, and economic viability of the process.
For example, in U.S. Pat. Nos. 5,711,817 and 5,879,637, the raw waste materials being processed will contain, for example, a percentage of lignin that is refractory at the temperature and pressure employed in the hydrolysis process, and therefore, will not hydrolyze. Accordingly, the contaminant, e.g., lignin, produces a strong by-product waste stream that must be dealt with upon completion of the processing steps through the GPV in an efficient manner, again, creating increased costs and reducing efficiency.
In the past, emphasis was placed, first, on attempting to use wastewater treatment processes and apparatus to control the accumulation of dissolved organic debris in the recycled water used for these processes, and second, on attempting to mitigate the undesired emission of fossil fuel air emissions from steam generators required to sustain the endothermic reactions necessary for these processes. To date, it is believed no attempts have been made to extract or mitigate the accumulation of dissolved toxic metals introduced from the feed materials to be processed. Such practices were believed to be counterproductive to the usefulness of the processes.
Nevertheless, GPVs provide a suitable environment with respect to temperature and pressure for conducting and enhancing either of these reactions, i.e., wet oxidation or hydrolysis. By oxidizing via wet oxidation, or separately, hydrolyzing via very mild acid hydrolysis, particular organic materials, the materials can be more easily separated from other components, such as toxic metals, and the like, and as a result, with further processing, desired materials, such as ethanol, lactic acid, and the like, can ultimately be produced from the initial raw waste materials.
Another shortcoming in the existing art with respect to GPVs is the difficulty in beginning the continuous process from a cold start. In U.S. Pat. No. 4,792,408, this shortcoming is obviated by the use of an isolated burner that produces water from combustion products that must be extracted. In U.S. Pat. Nos. 3,853,759, 5,711,817 and 5,879,637, this shortcoming is obviated by the use of steam and hot water injected at the peak pressure location in the vessel. The delivery of enough steam to sustain the entire thermal heat energy needs of these processes is inefficient to the point of detraction from the otherwise useful character of those inventions.
The most commonly used commercial technique by which the heat transfer surfaces for internal heat energy recovery are maintained clean in a GPV is set forth in U.S. Pat. Nos. 3,853,759 and 4,272,383. These patents disclose the use of a nitric acid solution to dissolve undesired mineral deposits that commonly form on the heat transfer surfaces of the GPV. It is these mineral deposits that detract from internal heat energy recovery. In other words, mineral deposits formed on the surfaces of the GPV separating the outer, incoming downward-flow raw waste materials feed stream from the inner, upward-flow processed stream prevent heat energy from being more fully conveyed from the hotter processed stream to the cooler raw waste materials feed stream while in operation. Using the nitric acid solution procedure, however, causes the GPV to be closed or shut down to normal operations for as much as 20% of the available operating time. Moreover, it is well known that the handling and use of nitric acid presents serious safety and environmental issues.
Other patents, such as U.S. Pat. Nos. 5,030,291 and 5,080,720, describe mechanical devices to enhance internal heat energy recovery in a GPV, i.e., to clean the GPV. However, these patents disclose mechanisms that are used only periodically. In contrast, the need for cleaning a GPV, to the degree required to sustain the heat energy requirements of the GPV in relying in greater part on the exothermic oxidation of a small percentage of the total organic materials flowing in water, is continuous.
The manner of cleaning a GPV disclosed in U.S. Pat. Nos. 5,030,291 and 5,080,720 requires a minimum gap between the GPV tubulars of about one inch (2.54 cm) to allow the passage of the device to clean the apparatus. It is also observed that the cleaning device employed by these patents will have difficulty cleaning the recessed mixing zones or restricted gaps of the present art GPVs. Further, U.S. Pat. No. 4,272,383, which teaches nitric acid cleaning, cannot accommodate cleaning in that manner if the minimum space between tubulars has been closed by the lack of centering the tubulars in the apparatus in addition to the difficulty of cleaning recessed mixing zones.
One currently available technique for inducing acid hydrolysis in a GPV is described in U.S. Pat. Nos. 5,711,817 and 5,879,637. While the reaction time of the waste materials in the process stream may be varied by changing the rate of flow of the process stream carrying the materials through the GPV, there is no way to change the distance between the flow point of initiation of the hydrolysis reaction and the flow point of quenching the hydrolysis reaction without physically removing the central core of the GPV and physically cutting and changing the length of the tubular between the points of initiation and quenching. Likewise, these same references refer to processing techniques whereby a dense acid, such as sulfuric acid, can be managed in the form of a hydraulic column partially flooded with waste or water, and partially air gapped. Such a processing technique can cause irregular bursts of flow of acid into the reaction chamber in the bottom of the GPV.
Thus, there remains a need for improvements to GPVs, and related processing methods, whereby the processing of organic wastes by the partial exothermic wet oxidation of a percentage of the waste materials feed stream can be made effective and useful by enhanced internal heat energy recycling within the GPV. Specifically, there remains at least a need for an improved GPV and a related method for the surgical sequential use of partial wet oxidation of dissolved organics, including the processing of dilute waste materials in water suspension, to enhance the very weak acid hydrolysis of the remaining cellulosic fibers in the waste materials that were refractory to the wet oxidation process, while mitigating the potential adverse effects of dissolved metals and non-productive hydrocarbons.
In turn, such a GPV and related method will also create a need to exclude certain materials from the GPV. For example, in many flow streams containing raw waste materials, certain dissolved materials, such as disaccharides and mono-saccharides, may exist therein that would be damaged by the introduction of oxygen that attacks undesired, dissolved toxic metals, lignin, and the like. Consequently, a need to separate these materials before they enter the GPV and, desirably, to reincorporate them into the process stream, after the reaction processes in the GPV, also remains.